As an alternative to fossil fuel, hydrogen is being trialed, wherein a major challenge consists in the storage and release of the hydrogen. A very promising approach is the use of regenerable, liquid hydrogen carrier materials (Sobota, M., Nikiforidis, I., Amende, M., Zanón, B. S., Staudt, T., Höfert, O., Lykhach, Y., Papp, C., Hieringer, W., Laurin, M., Assenbaum, D., Wasserscheid, P., Steinrück, H.-P., Görling, A. and Libuda, J. (2011), Dehydrogenation of Dodecahydro-N-ethylcarbazole on Pd/Al2O3 Model Catalysts. Chem. Eur. J., 17:11542-11552. doi: 10.1002/chem.201101311). Liquid hydrogen carrier materials are also described in DE 10 2008 035 221 A1 and EP 1 475 349 A2. For the storage of hydrogen in liquid hydrogen carrier materials, a chemical substance is needed which can assume a reversible energy-rich and energy-poor state. This occurs through catalytic hydrogenation and dehydrogenation of the substance. A substance which can advantageously be used for these reactions can thus serve as a hydrogen storage substance (Teichmann, D., Arit, W., Wasserscheid, P., Freymann, R.: A future energy supply based on Liquid Organic Hydrogen Carriers (LOHC); Energy and Environmental Science, Issue 8, 2011).
LOHC systems known in the prior art are as a rule pairs of substances in which the energy-poor substance A is a high-boiling, functionalized aromatic compound, which is hydrogenated in the energetic loading process. One example relates to the use of the substance pair N-ethylcarbazole/perhydro-N-ethylcarbazole, with which the energy loading can typically be performed at about 140° C. and elevated pressures and the energy unloading at temperatures between 230 and 250° C.
In said systems, the energy-rich substance perhydro-N-ethylcarbazole has a hydrogen capacity of about 6 mass % hydrogen. Thus the energy in the releasable hydrogen from 100 kg of perhydro-N-ethylcarbazole suffices to move a motor vehicle about 500 km, during which in the energy utilization on board water vapor is almost exclusively formed as the combustion product. Thus the approach presents a technically interesting alternative to other energy storage concepts for mobile applications.
A class which is also interesting for this application is represented by heat transfer oils, such as for example dibenzyltoluene, which can be catalytically hydrogenated at temperatures over 260° C. Such substances are known from Brückner, N., Obesser, K., Bösmann, A., Teichmann, D., Arlt, W., Dungs, J. and Wasserscheid, P. (2014). Evaluation of Industrially Applied Heat-Transfer Fluids as Liquid Organic Hydrogen Carrier Systems. ChemSusChem, 7: 229-235. doi: 10.1002/cssc.201300426.